FSSS

FURNACE SAFEGUARD SUPERVISORY SYSTEM

. For 210 MW Unit at Koradi.

FSSS SYSTEM

• 1. CLASS ROOM SESSION– UNDERSTANDING BASIC CONCEPTS & LOGICS OF FUEL FIRING.

• 2. SITE VISIT- PRACTICAL IMPLEMENTATION OF THE SYSTEM.FUEL FIRING EQUIPMENTS,CONTROL DESK(operation of equipments), RELAY PANELS,ALARM

& INDICATION .

FURNACE

• 1. CONSTRUCTION

• 2.OPERATION

• 3.MAINTENANCE

• 4.INTERLOCK & PROTECTION- (LOGICS & CONCEPTS.)

Furnace associated terminologies

a. Hanging Structure. b. Elevation- AB,CD,EF & Corner- 1,2,3,4. c. Wind box-A/B. d. Scanner fans- Auxiliary Dampers e. Burner Tilt- 13 Compartments. f. Tangential fuel firing system- Fire ball at the centre g. Igniters- h. Fuel System- FO, LDO, Oil guns, Hydro motor valves. Instrument air & Service air system i. Soot blowing system.

BOILER

• CONSTRUCTION- Mechanical • AUXILLIARIES Associated with – ( Interlocks & Protections of auxiliaries)• OPERATION & Control of Boiler.• FUEL FIRING SYSTEM- Equipments & Control system-(FSSS)

FUEL FIRING EQUIPMENTS-

• MECHANICAL EQUIPMENTS & THEIR CONSTRUCTION

• CONCEPTS & LOGICS INVOLVED IN FUEL FIRING SYSTEM

• INTERLOCKS & PROTECTIONS INVOLVED

• SEQUENCE OF OPERATING FUEL SYSTEM.

EFFECTIVE FUEL FIRING– MEANS PROPER COMBUSTION

• FURNACE HAZARDS-

EXPLOSION -- IMPLOSION

• NFPA 85-The National Fire Protection Association (NFPA) codes, such as

NFPA 85: Boiler and Combustion Systems Hazards Code are dedicated to fire and furnace explosion and implosion protection

• For proper combustion of fuel in the furnace , adequate supply of air must be supplied and intimately mixed with a supply of combustible material ( FUEL ) which has been presented in the correct condition.

• HOW TO AVOID?• Boiler Furnace explosion may be avoided by

timely purging and stoppage of leakage of fuel oil in furnace.

Practical means of avoiding furnace explosion is the prevention of an explosive accumulation

• Furnace explosion is rare, but very severe in nature. This situation exists because furnace is supplied with explosive accumulation.

• Just a minute part of those explosive charges receive sufficient ignition energy to actually cause an explosion.

• The Furnace explosion requires both sufficient explosive accumulation and sufficient energy for ignition

CAUSE OF EXPLOSION- FURNACE PRESSURE-• Why to maintain furnace pressure ? • Furnace Pressure is one such very important parameter,

which needs continuous control, protection & monitoring. This is very important from safety of the boiler.

• In case of very low and very high pressure, the furnace may subject to explosion and implosion, which may result in Boiler Structure and pressure parts, tubes damage and furnace deformation.

• Explosion Factor = (Mass/Furnace Volume) x Composition Change/Elapsed Time)

The furnace explosion occurs due to:

a) Improper purging of the furnace and air.b) Inadequate ignition procedures.c) Maintaining fuel supply for too long a

period without establishing combustion. d) Re-lighting burners too soon after

previous flame out.e) Introduction of main fuel without ensuring

adequate ignition energy.

FURNACE IMPLOSION• CONDITIONS UNDER WHICH FURNACE IMPLOSION WILL

OCCUR-

• 1)Boilers with both induced and forced draft fans may become unbalanced especially if the forced draft unit becomes tripped and the induced fan unit remains in full operation.

• The induced draft fan will produce an excessive draft in the furnace and create the real likelihood of furnace implosion.

• Negative pressure excursion of sufficient magnitude to cause structural damage.

• Incase of ID Fan is capable of producing more suction head than the boiler structure is capable of withstanding.

• Control malfunction and / or operator error, establish such conditions.

• 2) The other process called flame collapse or flameout effect. The negative pressure excursion following a fuel trip and loss of furnace flame, in order to realistically evaluate pit falls and prevention techniques

CONDITIONS FOR PROPER COMBUTION OF FUEL

• It is the purpose of the burner to present the fuel in suitable condition for proper combustion.

• Generally this means atomizing the fuel and giving it some axial (for penetration) and angular (for mixing) velocity.

• For effective atomization the viscosity of the fuel is critical.• For fuels heavier than gas or diesel oils some degree of heating is

required.• It should be noted that the temperature of the fuel should not be

allowed to raise too high as this can not only cause problem with fuel booster pumps but also can cause flame instability due to premature excessive gasification.

• The smaller the droplet size the greater the surface areas/volume ratio is, this increases evaporation, heating and combustion rate.

DIAGRAM OF HOW THE FUEL BURNS INSIDE THE FURNACE?

TYPE OF FUEL- LDO (LIGHT DIESEL OIL )

FO (FURNACE OIL )PULVARISED COAL

Equipments involved- 1.IGNITOR-

TRIP VALVES, HEA IGNOTOR ASSEMBLY- SPARK ROD * SPARK TIP

EXCITATION TRANSFORMER. & CKT.

IGNITOR AIR FANS- FOR PROVIDING COOLING AIR TO IGNITOR TIP

2.OIL GUNS-

• TRIP VALVES- OIL HYDROMOTOR VALVES- PNEUMATIC VALVES

• ATOMISING VALVES- STEAM & AIR

• SCAVENGE VALVES-

3.PULVARISED COAL-

– COAL MILL- Ignition Energy availability condition.

– COAL FEEDER- To regulate amount of coal input in the Furnace.

– HAG & COLD AIR DAMPER

4.AIR SYSTEM- 13 COMPARMENTS

• WINDBOX TO FURNACE DIFFERENTIAL PRESSURE MONITORING.

• AUXILLIARY AIR DAMPERS- Modulating to control AIR flow

5.FLAME MONITORING SYSTEM-

• BURNER TILTS- To maintain temp.& Keep fire ball at centre.

SCANNERS- Flame scanners used to sense flame in boiler

to detect flame failure to avoid boiler furnace Explosion. Flame Scanners & Fire ball scanners.

6.SCANNER System-

• SCANNER LOGIC-

• IGNITION ENERGY

• FLAME FAILURE TRIPPING

Flame intensity

How the Fuel is Fired in Furnace?

Coal firing

FSSS System— Furnace safeguard supervisory system

This system supervises the Furnace operations, controls process parameters & Protects the Furnace under abnormal operating conditions.

The functions of FSSS mainly include: 1. To Safe guard the Furnace against “Abnormal operating conditions.”

2. To Supervise the condition of furnace during fuel firing .

INTRODUCTION

Furnace safeguard supervisory system popularly called FSSS

continuously monitors the operations related to fuel admission and

some other vital parameters to ensure safety of the Boiler.

Generally furnace oil or any kind of fuel is susceptible to

explosion hazards. Majority of explosion occurs during start up, shut

down and low load operations. There are many steps that must be

followed by the operator to admit a fuel in to the furnace safely and

properly. In high capacity boilers, where fuel input rate is very high

major furnace explosions can result from the ignition of un-burnt fuel

accumulated in the first one or two seconds. Human reaction time to

such situations is inadequate. So there a proper burner management

system called as FSSS is installed in the Boilers. Every operation related

to fuel admission is accomplished through FSSS

Advantages of FSSS system –

a. Continuously monitors the operations related to fuel admission & vital parameters, to ensure safety of

boiler.

b. Every fuel is susceptible to Explosion hazards. Majority of explosions occurs during start-up, plan Shut-down, & Low load conditions.

c. Boiler operator has to take many important & sequential steps to admit fuel in the furnace, safely & properly . If it is left to the judgment of the operator, then high probability of error will be involved. This system helps to reduce the error.D Accuracy of Ignition energy is an important factor for proper combustion of fuel. E System logics allows / Dis allows fuel admission in the furnace by monitoring furnace condition.

FSSS Helps us to provide:---

Monitoring OF processes parameter

Control & Protection OF processes parameter whenever IT deviates from its normal value.

System logics senses dangerous situations & does not allow Fuel admission in such situations & thus protects the furnace, if reqd, by giving trip commands to boiler.

What is meant by Boiler trip ???

Every type of Fuel is cut-off from the Furnace . NO Flame condition is established..

FSSS System consists of -- Hardware & Software.

Hardware

Panels in control room - Consists of Relays, Timers. Control Desk-- -For operation of fuel firing equipments. (For Monitoring & Control of parameters )

Indication & Alarm system.— For alertness & actions.

UNIT PANEL- 1

UNIT PANEL-2

AB Elevation

CD Elevation

EF Elevation

Coal mill “A”

Coal mill “B”

Coal mill “C”

Coal mill “D”

Coal mill “E & F”

FSSS Panels lay-out :- (For Relay based system )

Software-- Electrical drawings- (Logic Diagrams. )

Supply system---220 V DC & 110 V AC

1) 110 v ac FROM IPDB ( Instrument panel distribution board.) used for relay logic system.

2) 220 V DC FROM DCDB ( DC distribution board), for relay logics & “TRIPPING Logic”.

3) 24 V DC for Indication supply. (Console indications)

What are the Abnormal operating conditions ?

Flame failure,

Furnace pressure inadequate-High / Low.

Loss of fuel.

Air flow less than 30%.

Sudden tube leakage.

What needs to be Monitored during fuel firing ?

Flame condition monitoring by flame scanners.

Total air flow monitoring.

Furnace pressure.( Negative )

Secondary Air flow ( Wind box to Furnace DP )

Oil pressure & Feeder speed.

Oxygen % in flue gas.

Drum level

Feed flow & Steam flow.

Which are the Auxiliary system associated with Furnace?

Air flow system. ( Primary & Secondary )

Oil flow system :- (Light oil & Heavy oil )

Coal feeding system.

Feed Water system.

Any Negative Impact on these systems will affect the working of Furnace.

Interlocks & Protections are provided for safe working-

What is meant by

Interlocks & Protections ?

1. Air flow system. ( Primary & Secondary ):- PA fans are used to provide primary air.

Hot air takes coal as fuel from mill to furnace at all the elevations. This requires sufficient Header Pr.

If the Header pr. Drops to certain level ,then we need to trip lower mills. Reasons for pr. Drop will be confirmed, corrective actions will be taken to restore the header pr. to normal value. If it is due to tripping of PA Fans , then it will be difficult to run furnace. So Boiler will be tripped.

FD Fans are used to provide secondary air.

This air is used to help complete combustion of fuel.& maintain Tangential Firing ,to keep fire ball at the centre.

DP is maintained between Windbox to Furnace.

Secondary air also helps to maintain Furnace Draft.

If FD Fan trips ,due to any reason,then interlock is provided to trip corresponding ID Fan.

This air is also used to cool scanners through scanner fans.

2. Oil flow system :- (Light oil & Heavy oil )

Light oil is used during initial light-up of furnace, to bring Sufficient ignition temp.for firing Heavy oil.

“Light oil fuel flow” &” Temp adequate” are the required conditions, used as interlocks.

Heavy oil is used, to bring Sufficient ignition temp.for firing Coal .Naturally Heavy oil Temp adequate” is the required condition, used as interlock.

Four guns are used at each elevation. When-ever ¾ guns are working properly,Ignition permit is given to fire coal as fuel, as it brings the ignition temp. for coal to burn completely.

3. Coal feeding system.:-

•Pulvariser ready condition is reqd.

Conditions reqd for Pulvariser ready:-

Pulv. Outlet temp not high, cold air valve open.

Tramp iron valve open, seal air valve open.

feeder start permissive, NO PA trip, NO pulv.stop.

Pulv. discharge valve open.

Hot air gate to be open. ( Proper opening of hot & cold air dampers )

•Coal feeder need to start.

• Feeder speed to raised as per requirement of load.

4. Feed Water system. :-

Low load line valves operative.

Main line valves operative

ELP & BFP ready to start.

Drum level auto control healthy.

Drum level Protection in service.

PURGE READY INTERLOCK FOR BOILER:-

CONDITIONS REQD.:-

All Heavy /Light oil valve closed.

Flame scanners indicate NO Flame

All feeders off/ All pulverisers off.

No boiler trip

All HAG closed

All aux.dampers modulating.

Major FSSS INTERLOCKS:-

•Elevation load < 30 %.

•Loss of AC at any elevation in service.

•Loss of DC Supply for > 2 secs.

{ unit trips while restoring the DC supply. )•Heavy oil temp. adequate.

•Burner tilt horizontal

•Air flow less than 40 %.

•Drum level high / low.

•ID /FD fan off.

Heavy oil supply pressure adequate.

Limit switch contact for Trip valve open.

LDO fuel supply pressure adequate.

LDO header pressure low.

Atomising air / Steam pressure low.

.Aux. air dampers modulating. Scanner fan ON

.HOTV valve open

PA pressure low

FD / PA trip.

Pulv / Feeder ON

Seal air valve open

Pulv.outlet temp high.

Hot air gate open.

Scanners show FLAME

OIL valve open,Atomising valve open.

S.N. Boiler Trippings Effects.

1 Drum level very high. To prevent Entry of wet steam in Turbine,

2. Drum level very low. To avoid boiler starvation

3 Furnace draft inadequate(V.High /V. low )

To safeguard furnace from excessive stresses.

4 Total air flow & boiler load less than 30 %.

To ensure sufficient air for combustion during start up activity.

5 Flame failure trip To avoid admission of coal when sufficient ignition energy is not available.

Boiler protections :-

Flame failure trip To avoid admission of coal when sufficient ignition energy is not available.

Loss of all fuel trip. To ensure re-admission of fuel only after furnace is Purged.

Both ID trips. No means of driving out flue gases to avoid operation of furnace in such situations.

Both FD trips. No supply of air for combustion.

Loss of supply to FSSS logic system

To prevent boiler operation ,if safeguard system is not functioning.

Mannual trip Push buttons pressed.

For manual trip when-ever reqd.

Turbine trip Interlock tripping.

Furnace temp. very high

Excessive heating of reheater tubes.May cause tube failure.

Implosion damper open To prevent development of excessive – ve pressure in the furnace.

FUEL FIRING ACTIVITY

START & STOP. (LIGHT UP & WITHDRAWAL OF UNIT)

FIRE KILLING OPERATION-

UNIT WITHDRAWAL ACTIVITIES

WHICH ARE LIGHT UP ACTIVITIES ?

PURGING,- Purging is done to clean furnace from combustible gases by running ID Fan and FD Fan at atleast 30% load for 5 minutes to avoid Furnace explosion.

OPENING OF TRIP VALVES, MONITORING OF OIL PRESSURE & ,FLOW,ATOMISING MEDIUM HEADER PRESSURE.AUXILLIARY AIR CONTROL SYSTEM, WIND BOX TO FURNACEDIFFERENTIAL PRESSURE..Firing of ignitors Taking of LDO oil guns- OPENING OF OIL VALVES,ATOMISING VALVES.,

CHECKING STABILITY OF FLAME SCANNERS.

MONITORING FURNACE TEMP,

PROVING HIGHER ELEVATION OIL GUNS.

DEVELOPING REQUIRED DRUM PRESSURE FOR ROLLING PURPOSE.

COAL MILLS,COAL FEEDERS,HAG & DAMPERS CONTROLS

Light up Activities Preparedness

FURNACE PURGE:-

Furnace purge is required after a boiler trip out, before relighting the boiler to expel all unburnt full particles, vapor etc, form the boiler so that when spark is introduced during light up, possibility of explosion are avoided.

FSSS ensure a proper furnace purge in following manner:- “Purge Ready” signal when appear only when following conditions are fulfilled.110V AC and 220V DC supply to FSSS panel is switch on.

Boiler Drum water level normal.

At least one ID and one FD fan running.

Establish 30% full load air flow as seen in total air flow

recorder.

Igniter trip valve closed.

Warm up trip valve closed.

Heavy oil trip valve closed.

All igniter valves closed.

All warm up and oil gun valve closed.

All auxiliary air damper modulating to maintain air flow can

adequate wind box to furnace differential processing?

All coal mills off.

All raw coal feeders off.

All flame scanners show no flame.

All mill hot air gates closed and cold air damper are less

than 5 degree open.

No boiler trip command.

When above conditions are met, signal “purge ready”

will disappear, even during purging process. When signal “purge

ready” appears, press button “push to purge after the expiry

of purging time signal “purge complete” appears.

LIGHTING UP WARM UP ELEVATION

Now we are ready for Boiler light up.

a) Lighting up warm up elevation ABElevation AB has capability to be used for either burning light

oil or heavy oil. So select “light oil” on the consol for AB elevation ensure warm up oil tips are provided is guns of that particular elevation.

b) I] Igniter trip valve: Press igniter trip valve “open” push button igniter trip

valve oil open provided the following condition are fulfilled.Igniter oil supply pressure adequate (more than 12.1 kg/cm2)All igniter valves closed.No boiler trip command.

In addition, instrument air supply must be available to actuate trip valve.

If igniter fan is not started, it will start when first igniter start Command is given.

II] Opening light oil trip valve:Light oil trip valve will open if following condition is met:

No boiler trip. Elevation AB LO valves on guns is closed.

Light oil pressure adequate i.e. they should not less than 1.4 kg/cm2 for more than 25 sec. and light oil trip valve open push button pressed.

The following figure shows logic diagram for “warm up oil trip valve control”. Before Boiler light up with Light Diesel oil, LOTV must be open by giving “open” command from push button switch on the desk.

Output form “OPEN” push button switch goes to an AND gate. Other input to this gate are_

1. No Boiler Trip2. All Corner Valves closed3. LDO Pressure Adequate4. LOTV “Close” command not persisting

When all these inputs are TRUE, OPEN command causes AND gate to give a TRUE output causing LOTV to open.

LOTV closes when

Close command through push button switch is initiated OR

Boiler trips OR

After a delay of 3 second when any warm up oil elevation’s Corner valve is NOT CLOSE AND

If LDO Pressure drops to LOW valve OR

If P between atomizing air and LDO is low.

Starting Igniter:When igniter is started for 1st 10 sec period, oil and atomizing

air are admitted though the valve and simultaneously a spark is applied. The spark lights up the oil spray and flame is sensed by flame sensor in the igniter. This happen within 10 secs, the valve is held ‘open’ allowing igniter to continue.

There are no separate igniter start push buttons, pressuring any one pair of oil gun start or stop push button will give starting impulse to all four igniter of that elevation. To start the oil guns press either 1and 3 or 2 and 4 start button. This gives commands for igniter start provided the following condition is met:

DC power available. No boiler trip command. Burner tilt horizontal and air flow less than 40%. Igniter trip valve open. L.O. trip valve are open.

Igniter start causes following gives a start command to spark plug. This command holds for 10 secs by which time if flame is in the igniters.

Now in this way at least three igniters on selected elevations are proved command is given for selected LO guns to advance and light up provided:

o Atomizing air valve openo Warm up oil valve open.o Corresponding igniter proved.

Under this condition, first one gun will advance, atomizing air will open the next gun of will undergo similar operation with time log off 25 secs in this at least three guns have to be proved, otherwise oil guns will trip out. When guns trips , the gun will not retract , it must be retracted locally immediately to avoid any fire accident. Warm up guns will trip under following conditions:

Pressing stop push button. Moving local switch from ‘Remote’ to any other position. Gun advanced or engaged limit switches are released. Corresponding igniters trip out. Air or oil is elevating valve are closed. Oil valve is not proven to be open within 90seconds. Any boiler trip command. At any time when warm up guns are in service, it more than one

igniter is off all warm up guns oil trip.

LIGHTING UP HEAVY OIL ELEVATION

I] Lighting up Heavy Oil Elevation.

Healy oil can be fired on any three elevation AB,CD and EF.

Heavy oil guns are supposed to be self sustaining. Once three oil

guns are tilt, their flow (gun loading in that particular elevation) is

more than 30% or Boiler load more than 30% and flame scanners are

sensing flame under these condition light oil can be withdrawn

without affecting oil guns.

II] Now the heavy oil valves open under following condition

are met. Header oil pressure adequate. All heavy oil hydra motor valve of AB, CD, EF oil guns are

proven closed. No boiler trip command. Heavy oil pressure not low less than 1.4 kg/cm2 for more than 2

secs.

When valve open signals open appears on the panel.

Starting igniter command oil materialize only when heavy oil is ready for light up with oil temperature more than 1050C .

Now taking heavy oil guns service in elevation AB.

Gun will advance provided:

Atomizing steam isolating valve open. Heavy oil manual isolating valve open. Heavy oil igniter on.

Under this condition oil gun advance.

When valve open signals open appears on the panel.

Starting igniter command oil materialize only when heavy oil is ready for light up with oil temperature more than 1050C .

Now taking heavy oil guns service in elevation AB.

Gun will advance provided:

Atomizing steam isolating valve open. Heavy oil manual isolating valve open. Heavy oil igniter on.

Under this condition oil gun advance.

MILLFSSS controls the salve starting, running and stopping

of mills.

Pulverizer Ready for start

This is common to all six mills signal Pulverizer ready will appear when all the following conditions are fulfilled.

Mills outlet temperature is less than 900C. Seal air valve open. Cold air gate open. Feeder inlet gate open. Pulverizer discharge valve open. Tramp iron hopper gate open. No Pulverizer trip command. Burner tilt horizontal and air flow less than 40% for

subsequent mills, the first R.C. feeder ON. Energizes relay by passing burner tilt and air flow conditions.

Ignition permissive :

It is presumed that P.A. fan is running, seal air fan is running, P.A. header pressure is normal before we can actually start the mill, another conditions that of providing sufficient ignition energy near the burner nozzle of the mill has to be ensured so that, once coal flow is established through mill, the pulverized coal will light up inside the boiler without any loss of time.

At least three oil guns (Heavy oil or warm up) are in service for the first mill to be started A or B, C or D, E or F.

For second mill to be start ignition energy is given by either:- Three oil Guns being in service adjacent to mill or Boiler load is more than 30%. Adjacent mill running with RC feeder speed in excess of 5rpm or

Pulverizer A or C in service at igniter than 50% loading. This ignition energy must be continuously available for three

minutes after starting RC feeder.

Even though the logic permits removal of ignition energy after three minutes operationally it will be required for even longer period till boiler flame conditions are stable.

The following figure shows Logic Diagram for Ignition Permissive

for Pulverizer A and B. Similar requirements are applicable for

other Pulverizers:

1. Pulverizer B is running with 50% loading AND Boiler Load is More than 30% OR

a) Elevation AB in service with 3 out of 4 Guns established.

2. Pulverizer B Ignition Permissive is available if

a) Pulverizer A or C running at 50% loading AND Boiler load is more than 30% OR

b) Oil Elevation AB in service with 3 out of 4 Guns established.

Actual starting of the millIf conditions are met and if local key release push button is

released mill can be started by pressing the start push button on console.

As soon as mill starts, cold air damper opens full. Hot air gate can now be opened provided temperature after mill

still remains less than 900C. If the temperature exceeds 900C, the white signal ‘ Pulverizer ready’ will disappear but the mill will continue to run. Pulverizer ready can disappear for other reason also.

However if discharge damper closes mill will trip immediately.

After opening the hot air gate, cold air and hot air damper can be regulated to achieve an after mill temperature of 600C

to750C and P.A. fan flow about 52 T/hrs. During manipulation of air, take care load P.A. fan so, that P.A. header pressure does not fall below 650mm.

If the ignition energy continuous to be present after starting mill, feeder can be started and mill loaded.

As soon as feeder is started, signal given to panel to modulate fuel air accelerator to speed of feeder. When feeder stops, fuel air damper is shut. This is to facilitate quick light up of fuel when a mill is started.

After 50 seconds of feeder starting relay energizes to permit feeder to be controlled by boiler pressure auto.

PULVERIZER START

When ignition energy available and Pulverizer ready condition are establish for the respective Pulverizer. The Pulverizer may be place in service as follows:

a) Start the Pulverizer by pressing start push buttonb) When Pulverizer is proven on as indicated by its on indication or by

amp on UCR open, hot air gate and allow pulverize to come adequate temp (750C) and PA flow of about 52 T/hr with the help of cold air damper.

c) When Pulverizer is up to temp 1400C start feeder and set at minimum and associated elevation of fuel air damper proven close.

Coal flow must be proven either by coal flow detector or satisfactory Pulverizer amp within 5 secs after feeder started. When minimum of the two feeders are establish at greater than 50% loading, associated elevation of oil guns may be shutdown provided feeder has been on for minimum 3 of 3 minute.

FAN CONTROLIgniter and scanner fans:

Igniter fan:-

Igniter can be started from control desk otherwise it get set started automatically when any igniter or oil elevation start is initiate at least one ID and more than one FD fan must be service for the igniter fan to start on stopping igniter fan from control desk will remove the associated igniter fan service provided all of igniter valve are closed.

Scanner Fan Control:-

It can be started from control desk otherwise it get started automatically when the scanner air duct to differential pressure falls below 4.5”w.g. low differential pressure more than 10 secs will alarm, the scanner emergence damper open on interlock when both ID/FD fan are off, this allows the fan to draw ambient air for the cooling scanner when unit is bottled up on stopping fan from control desk will remove the scanner fan from service provided the scanner duct to furnace desk. Pressure is above 4.5”w.g.

CONTROL of THE WIND BOX DAMPERS

1] Auxiliary Air Dampers:During furnace purge and when load is less than 30%. FSSS

modulates are auxiliary air dampers to maintain a low wind box pressure (30mm).

When load increases beyond 30% the modulation is for a higher wind box pressure (60mm), which is achieve by closing dampers near elevation not in service.

When warm up oil is in service, the auxiliary air damper of AB elevation opens to a predetermined position.

When heavy oil is in service, the auxiliary air is allowed to be controlled by opening depending on oil pressure.

When one FD fan trips, then all auxiliary and fuel air damper open wide.

 2] Fuel air dampers:All the air dampers are shut on elevations where there are no

feeders in service.After starting of feeder, the fuel air damper of that elevation is

allowed to be controlled with feeder speed.

Software part-- Electrical Drawings---

SUMMARY: FSSS achieves---

Smooth boiler start –up.

Routine operations.

Withdrawal of boiler safely,when ever reqd.

Tripping in case of abnormal conditions.

HOMEWORK: INTERLOCKS & PROTECTIONS– ID-FD-PA-BFP

AUXILLIARY INTERLOCK PROTECTION

ID FAN Over current,Earth fault,Shot circuit,Locked Rotor,DifferentialFD FAN

PA FAN

BFP

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